The present invention relates to a split die tool set comprising top and bottom dies for the production of compacted parts out of powdered material, and to initially positioning a lower punch to define a chamber for receiving powder. Preferably the lower punch is initially positioned substantially flush with an upper surface of the bottom die. During filling the lower punch may be moved downward and/or the top and bottom dies may be raised to fill chambers adjacent each of the dies with powder. Alternatively, powder may be transferred after completion of the filling step by subsequently moving the lower punch downward and/or raising the top and bottom dies to transfer powder from a chamber adjacent the top die to a chamber adjacent the bottom die.
Devices to compact powder material for the production of sprockets and gears are known in the art. Tool sets with split dies are typically used to form such parts, particularly where the part has two or more rows of teeth that are offset or out of phase with respect to each other. Split die tool sets generally comprise a pair of opposed die and punch sets, each having at least one punch and a die defining respective chambers in each set. At least one of the dies is movable with respect to the other die from an open position in which the sets are separated to a closed position in which the dies are abutted with the respective die chambers in closed communication to form a closed mold cavity. Relative movement of the die and punches in each set is accomplished through movement of either the die or punches, or both, with respect to each other.
The method of forming the part using split die tool sets typically includes filling one or both die chambers with powder material, transfer of powder from one portion of the chambers to another to fill an offset in the part, compaction of the powder, and ejection of the part. One known method of filling the die chambers involves bringing the top and bottom dies to a closed position with the bottom punch defining a bottom die chamber, the top die chamber being in communication with the bottom die chamber, and the top punch being separated from the top die. A movable duct or feeder is brought into position between the top punch and the top die to drop powder into the top and bottom die chambers. A method of this type is disclosed in U.S. Pat. Nos. 3,773,446 and 3,891,367. The '446 patent discloses a complicated press mechanism to prevent bending of the top die when the bottom punch moves upward to compact powder to form the part. A plate presses against the top die during the compaction step to prevent bending that could otherwise occur due to the upwardly directed force of the bottom punch against an offset portion of the part not being counterbalanced by the downward force of a top punch in the top die. The reference discloses filling, compaction and ejection steps, but does not discuss transfer of powder from a chamber in one of the dies to a chamber in the other die even though an offset is present in the part. The '367 patent discloses forming a helical gear with a tool set that comprises a bottom die, bottom punch and core rod, and a top die and top punch. For the filling step, the top die is brought into closed position with the bottom die, the bottom punch forms the bottom of a chamber in the bottom die, and the core rod is raised so that its upper surface is level with the upper surface of the top die. The top punch is raised to its uppermost position and separated from the top die. After the filling step, the top punch is adapted to move downwardly to enter the top die so as to compress the powder in a compacting step. A guide is provided to cause the top punch to mate correctly with the top die as the top punch moves downward. This reference also does not discuss transfer of powder from one chamber to another even though an offset is present in the part.
Another method of filling the die chambers involves separating both the top die and top punch from the bottom die with the bottom punch in a position defining a bottom die chamber. A movable duct is brought into position over the bottom die to drop powder into the bottom die chamber. A method of this latter type is disclosed in U.S. Pat. Nos. 5,698,149, 6,099,772, and 6,318,986. These references disclose various ways of transferring powder from the bottom die chamber to the top die chamber so as to provide sufficient powder in offset portions to completely fill the chambers prior to a compacting step in which the part is formed. The '149 patent discloses moving the top die and top punch downwardly so that the top die engages the bottom die, and then relatively moving the bottom die and bottom punch with respect to each other to transfer powder from the bottom die chamber to the top die chamber. After the transfer step, one of the die and punch pairs is translated with respect to the other pair, either rotationally or laterally, so as to provide a phased offset in the part. The '772 patent discloses a tool set comprising a bottom die and two nested bottom punches movable with respect to each other and the bottom die. A chamber is formed in the bottom die and punch set by moving the bottom punches to their lowest positions. After filling, the top die and punch are moved downward to form a chamber having an offset with respect to the chamber in the bottom die. Transfer of powder from the chamber in the bottom die to the chamber in the top die is accomplished by moving the lowermost bottom punch upwardly to a position where its upper surface is level with the upper surface of the other bottom punch.
The '986 patent is a continuation-in-part of the '772 patent and discloses another tool set as shown in FIG. 5 thereof. The tool set comprises top and bottom dies, each having two nested punches movable with respect to each other. The top punches are separable from the top die so that the top die may be brought into contact with the bottom die. The top die has a chamber that forms an offset with respect to the chamber in the bottom die. The bottom punches are then positioned so as to form a chamber bounded by the bottom die. After filling the two die chambers, the dies are moved upwardly with respect to the bottom punches causing powder to flow between the dies. Due to a shoulder formed by an offset in the dies, powder may be carried upwardly with the bottom die to create a local high spot or hump above the shoulder. The top punches are then inserted into the top die with the innermost top punch raised relative to the outer top punch until the outer punch is correctly spaced from the shoulder. To ensure that the bridging of powder at undercut u (FIGS. 5a and 5b) is eliminated the innermost top and bottom punches are lowered relative to the outer bottom punch. At the same time the top and bottom dies move downwardly relative to the outer bottom punch until the punches and dies assume correct relative positions for initial compaction. This toolset requires additional steps to transfer powder between the die chambers.